I have a colleague who does "The House of Gallon" in 3rd grade. The kids really remembered it and were able to retell it to me so I could draw it on the board.

The big G is the house, 4 Qs are the windows, each window has 2 Ps for people looking out, and each person has 2 c's for eyes. They like it, they remember it...Must be a good one! I'm using this story this year.

I personally don't quite like the gallon man because its not quite anatomically correct. My kids can always understand the 4 quarts as limbs, but it's hard for them to "get" the pints and cups. Plus it doesn't explain that the other units of measure make up a gallon, in gallon man it all seems to be just an extension.